G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow

G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow by using mechanical effects

G01F1/10—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow by using mechanical effects using rotating vanes with axial admission

G01F1/115—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through the meter in a continuous flow by using mechanical effects using rotating vanes with axial admission with magnetic or electromagnetic coupling to the indicating device

a British company Filed Dec. 14, 1960, Ser. No. 7 5,848 4 Claims. (Cl. 73-231) This invention relates to iiow meters of the` type coinprising a rotor mounted within a conduit and arranged to coact with a transducer coil external to the conduit to generate electrical pulses at a repetition frequency determined by the rate ot oW of uid through the conduit and a counter for counting the pulses so generated.

One object of the invention is to provide a ow meter of the above type for use in measuring the tlow of liquids associated with air and which will discriminate between the passage of liquid andv air through the conduit.

The invention accordingly provides a iiow meter of the above specified type which includes means for sensing the nature of the iluid ilowing through the conduit and means controlled thereby for preventing the counter from registering the pulses from the transducer coil when air is traversing the conduit but permitting the counter to operate when liquid is traversing the conduit.

More specifically, the flow meter according to the invention includes a pair of probes in the conduit, an electronic oscillator which is coupled to the probes and controlled as to its effectiveness by the electrical resistance of the iluid iiowing through the conduit and a gate controlled by the oscillator for preventing the passage of pulses to the counter when air is traversing the conduit but permitting such passage of pulses when liquid is traversing the conduit.

Preferably the probes of the flowmeter are situated upstream of the rotor and this has the advantage that We avoid inaccuracies which might be caused by the lasf traces of liquid (eg. milk) being iiung by the rotor on to the probes on its down run in air. Preferably one of the probes is constituted by the wall of the conduit and the other is located at or near the centre of the conduit. No contact can then be made by the latter probe with any traces of milk travelling along the Wall of the conduit.

Normally the rotor of a ilow meter of the above type carries a magnet, on one of its blades near the tip thereof, which coacts with the transducer coil to generate pulses as the rotor is rotated by the fluid. This, however, is undesirable due to corrosion diiliculties when the dow of a liquid such as milk is to be measured. Another object of the invention is to provide an improved form of rotor such that the magnet is effectively maintained out of contact with the fluid but is nevertheless capable of generating strong signals in the transducer coil.

The invention accordingly also provides a liow meter of the above type in which a magnet is housed within the hub of the rotor with its magnetic axis extending axially of the rotor and in which the hub and blades of the rotor are made of magnetic material and so constitute, in elect, an extension of the magnet.

Alternative constructions of iiow meter embodying both of the above features and suitable for use with milk will now be described in more detail, by way of example, with reference to the accompanying drawings in which:

Referring rst of all to FIGS. 2 and 3 of thedrawings, a rotor 20 is mounted in a housing intended for connection in a pipe line through which the ow of milk to be measured takes place. The housing consists of a centre portion 21 and two end portions 22 held together by clamping rings 23. In the portions 22 of the housing are spiders 24 supporting bearings 25, 26 for the ends of the spindle 27 of the rotor. The rotor is formed with a hub 12 and blades 13 of magnetic stainless steel and within the hub 12 is enclosed, so as to be effectively shielded from the milk, a magnet 11, having its N-S axis on the centre line of the rotor. The blades 13 therefore constitute an extension of the. magnet and are effective to induce large signals in a. transducer coil 9 external to the conduit through which the milk ilows. Two probes 8,10 are provided for sensing the resistance of the tluid flowing through the housing, one being constituted by the portion of the housing surrounding the transducer coil 9, and the other by a bolt which retains the coil in position.

Referring now to FIGS. 1 and 4 of the drawings, the probes 8, 10 form part of the circuit of a Wien bridge oscillator 3 constituted by tubes V1 and V2. The iluid iiowing past the probes constitutes an effective resistance 7 between the probes. When air is flowing past the probes the resistance 7 is high, the oscillator oscillates and the A.C. output of the oscillator is fed to the gate 4, which rectities and smooths this output and applies a positive D.C. voltage to the grid of a tube V3 having a rectier in its grid circuit, so maintaining a high current through the tube V3 with the result that a relay RL in the anode circuit of the tube V3 is energized to cause a contact RL, to short circuit contacts C and D and so, as shown in FIG. 5B, prevent pulses from the coil 9 being passed to a counter 6. This may, as described in British specication No. 752,496, be an electro-magnetic counter preceded by a chain of electronic frequency dividers and a shaping circuit for shaping the pulses generated in the coil 9.

When, however, milk `flows past the probes 8, L10 in place of air, the resistance 7 decreases, the Oscillator ceases to oscillate, the current through the anode load of the tube V3 decreases and the relay RL opens the con tact RL1 to enable the pulses generated in the coil 9 to pass to and be counted by the counter, as indicated in FIG. 5A.

In the alternative construction shown in FIGS. 6 8, the rotor Ztl of the flow meter is again mounted in a housing consisting of abutting sections 21, 22, 122 held together by clamping rings 23. A male end fitting 45 -is provided on the upstream end section 22 and a female end fitting 46 forms part of the downstream end section 122 and this ensures that the ow meter will be correctly installed in the pipe line. In the housing are formed spiders 47 supporting bearings 26, 25 for the rotor. The blades 13 and hub 12 of the rotor are of magnetic stainless steel and within the hub is enclosed a magnet 11 having its N-S axis on the centre line of the hub of the rotor.

Fitted to the exterior of the housing are two laterally projecting sleeves 21, 41. In the sleeve 21 is mounted a transducer coil 9, which is connected to the electrical circuit of the ilow meter by leads 42 and which is removably held in position by a screw cap 43. In the sleeve 41 is mounted a block 145 of insulating material, which has an extension 48 projecting inwardly towards the centre line of the housing and is held in place in the sleeve 41 by a screw cap 49. One air probe is constituted by the projecting tip-50 of a metal rod 51 mounted within the insulating block 14S. Leads 60 from the electrical circuit, which is as illustrated in FIG. 4, are connected to therod 51 and the sleeve 41. The other air probe is thus constituted by the inner Wall or the housing.

In addition to the advantages indicated above, the arrangement of air probes upstream of the rotor provides a far more rapid respon-se to the presence of air in the duid owing through the housing than the construction described with reference to FIGS. 1-5.

What we claim as our invention and desire toy secure by Letters Patent is:

1. A flow meter comprising a conduit, a rotor mounted within the conduit and arranged to bevrotated by passage of fluid through the conduit, a transducer coil external to the conduit which coacts with said rotor to generate pulses at a repetition frequency determined by the rate of ow of fluid through the conduit, a counter for counting the pulses generated by said coil, a pair of probes in the conduit, an electronic oscillator which is coupled to the probes and controlledv as to its effectiveness by the electrical resistance of the fluid ilowing through the conduit and a gate controlled by the oscillator for preventing the passage of pulses -from the coil to the counter when air is traversing the conduit but permitting such passage of pulses when liquid is traversing the conduit.

2. A ow meter according to claim 1, in which the probes are situated upstream of the rotor.

3. A dow meter according to claim 2, in which one of the ptro'bes is constituted by the wall of the conduit and the other is located at or near` to the centre of the conduit.

4. A ow meter according to claim 1, in which the oscillator is a Wien bridge oscillator which is maintained in oscillation when air is flowing past the probes and is caused to cease oscillation when liquid is owing past the probes.

Claims (1)

1. A FLOW METER COMPRISING A CONDUIT, A ROTOR MOUNTED WITHIN THE CONDUIT AND ARRANGED TO BE ROTATED BY PASSAGE OF FLUID THROUGH THE CONDUIT, A TRANSDUCER COIL EXTERNAL TO THE CONDUIT WHICH COACTS WITH SAID ROTOR TO GENERATE PULSES AT A REPETITION FREQUENCY DETERMINED BY THE RATE OF FLOW OF FLUID THROUGH THE CONDUIT, A COUNTER FOR COUNTING THE PULSES GENERATED BY SAID COIL, A PAIR OF PROBES IN THE CONDUIT, AN ELECTRONIC OSCILLATOR WHICH IS COUPLED TO THE PROBES AND CONTROLLED AS TO ITS EFFECTIVENESS BY THE ELECTRICAL RESISTANCE OF THE FLUID FLOWING THROUGH THE CONDUIT AND A GATE CONTROLLED BY THE OSCILLATOR FOR PREVENTING THE PASSAGE OF PULSES FROM THE COIL TO THE COUNTER WHEN AIR IS TRAVERSING THE CONDUIT BUT PERMITTING SUCH PASSAGE OF PULSES WHEN LIQUID IS TRAVERSING THE CONDUIT.